Gunhee Jang

Finite Element Analysis of a Coupled Hydrodynamic Journal and Thrust Bearing in a Computer Hard Disk Drive

This paper proposes a method to calculate the characteristics of a coupled hydrodynamic journal and thrust bearing of a HDD spindle motor. The governing equations for the journal and thrust bearings are the two dimensional Reynolds equations in and planes, respectively. Finite element method is appropriately applied to analyze the coupled journal and thrust bearing by satisfying the continuity of mass and pressure at the interface between the journal and thrust bearings. The pressure in a coupled bearing is calculated by applying the Reynolds boundary condition and compared with that by using the Half-Sommerfeld boundary condition. The static characteristics are obtained by integrating the pressure along the fluid film. The flying height of spindle motor is measured to verify the proposed analytical result. This research shows that the proposed method can describe HDB in a HDD system more accurately and realistically than the separate analysis of a journal or thrust bearing.

Development of a Linear Vibration Motor With Fast Response Time for Mobile Phones

Linear actuator has been widely used as vibration motor in mobile phones, and it generates a linear vibration through resonance in which the electromagnetic force with the application of a sinusoidal current excites the fundamental natural vibration mode of the moving mass-spring system. Figure 1 shows a linear actuator for mobile phones whose diameter and height are approximately 10 and 1 mm, respectively. The moving coil and mass are attached to a flat spring, and the radial magnetic field between the plate and the moving yoke is generated through a plate connected to the permanent magnet. The magnetic force in the air-gap between the plate and the yoke is generated according to Ampere’s law once the sinusoidal current is applied to the coil, and it excites the axial vibration mode of the linear actuator that generates the axial vibration. The linear actuators have a fast response time compared with other types of vibration motors. Currently, the response time of the linear actuators is approximately 50 msec, but the users and the application software of mobile phones are demanding increasingly faster response time. However, it is very difficult to reduce the response time while maintaining the vibration magnitude under the given constraints of volume and electric power.Copyright

Robust Optimal Design of the Magnetizer for a HDD Spindle Motor to Reduce the Harmonic Components of the Cogging Torque

Cogging torque of a brushless DC (BLDC) motor is a source of the vibration and noise of the hard disk drive (HDD) spindle motor, and the excitation frequencies of the cogging torques are the harmonics of the least common multiple of the poles and slots in ideal BLDC motors. However, manufacturing errors generate the additional harmonics to the cogging torque. Especially, the uneven magnetization of the permanent magnet (PM) in BLDC motors generates additional slot harmonics to the cogging torque. In small BLDC motors such as 2.5″ HDD spindle motors, the effect of additional slot harmonics is as serious as that of the fundamental harmonics of the cogging torque. A coil-positioning error of the magnetizer is a major source among the several potential sources of uneven magnetization of a ring-shaped PM in a HDD spindle motor [1]. It is difficult to estimate and to reduce the coil-positioning error when manufacturing a magnetizer. In addition, each magnetizer has different range of the coil-positioning error.Copyright